Diabetes is a condition characterized by high blood sugar (glucose) levels, and Type 2 diabetes is the most common form. Type 2 diabetes is a chronic disease, and left untreated, it can cause serious health complications. More than 29 million Americans have diabetes (the majority of which are Type 2), but 8 million don't know they have it, according to a 2014 report from the Centers for Disease Control and Prevention. And about 86 million U.S. adults have prediabetes, or blood sugar levels that are abnormally high, but not high enough to be classified as diabetes.